Sugarcane ethanol: Contributions to climate change - BAFF

4.2. Greenhouse gas balances
Biofuel conversion technologies
�e net emissions over the full life cycle of biofuels – from changes in land use to combustion
of fuels – that determine their impact on the climate. Research on net emissions is far
from conclusive, and estimates vary widely. Calculations of net GHG emissions are highly
sensitive to assumptions about system boundaries and key parameter values – for example,
land use changes and their impacts, which inputs are included, such as energy embedded
in agricultural machinery and how various factors are weighted.
�e primary reasons for di�ering results are di�erent assumptions made about cultivation,
and conversion or valuation of co-products. (Larson, 2005), who reviewed multiple studies,
found that the greatest variations in results arose from the allocation method chosen for
co-products, and assumptions about N 2 O emissions and soil carbon dynamics. In addition,
GHG savings will vary from place to place – according to existing incentives for GHG
reductions, for example. And the advantages of a few biofuels (e.g. sugarcane ethanol in
Brazil) are location speci�c. As a result, it is di�cult to compare across studies; however,
despite these challenges, some of the more important studies point to several useful
conclusions.
�is analysis notwithstanding, the vast majority of studies have found that, even when all
fossil fuel inputs throughout the life cycle are accounted for, producing and using biofuels
made from current feedstock result in substantial reductions in GHG emissions relative to
petroleum fuels.
In general, of all potential feedstock options, producing ethanol from maize results in
the smallest decrease in overall emissions. �e greatest bene�t, meanwhile, comes from
ethanol produced from sugarcane grown in Brazil (or from using cellulose or wood waste
as feedstock). Several studies have assessed the net emissions reductions resulting from
sugarcane ethanol in Brazil, and all have concluded that the bene�ts far exceed those from
grain-based ethanol produced in Europe and the United States.
Fulton (2004) attributes the lower life-cycle climate impacts of Brazilian sugarcane ethanol
to two major factors: First, cane yields are high and require relatively low inputs of fertilizer,
since Brazil has better solar resources and high soil productivity. Second, almost all
conversion plants use bagasse (the residue that remains a�er pressing the sugar juice from
the cane stalk) for energy, and many recent plants use co-generation (heat and electricity),
enabling them to feed electricity into the grid. As such, net fossil energy requirements are
near zero, and in some cases could be below zero. (In addition, less energy is required for
processing because there is no need for the extra step to break down starch into simple
sugars. Because most process energy in Brazil is already renewable, this does not really
play a role.)
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